public static Vector3 operator *(Quaternion q, Vector3 v)
{
// nVidia SDK implementation
Vector3 uv, uuv;
Vector3 qvec = new Vector3(q.X, q.Y, q.Z);
uv = qvec.CrossProduct(v);
uuv = qvec.CrossProduct(uv);
uv *= (2.0f * q.w);
uuv *= 2.0f;
return(v + uv + uuv);
}
public static Vector3 CalculateTangentSpaceVector(
Vector3 position1, Vector3 position2, Vector3 position3,
float u1, float v1, float u2, float v2, float u3, float v3)
{
//side0 is the vector along one side of the triangle of vertices passed in,
//and side1 is the vector along another side. Taking the cross product of these returns the normal.
Vector3 side0 = position1 - position2;
Vector3 side1 = position3 - position1;
//Calculate face normal
Vector3 normal = side1.CrossProduct(side0);
normal.Normalise();
//Now we use a formula to calculate the tangent.
float deltaV0 = v1 - v2;
float deltaV1 = v3 - v1;
Vector3 tangent = deltaV1 * side0 - deltaV0 * side1;
tangent.Normalise();
//Calculate binormal
float deltaU0 = u1 - u2;
float deltaU1 = u3 - u1;
Vector3 binormal = deltaU1 * side0 - deltaU0 * side1;
binormal.Normalise();
//Now, we take the cross product of the tangents to get a vector which
//should point in the same direction as our normal calculated above.
//If it points in the opposite direction (the dot product between the normals is less than zero),
//then we need to reverse the s and t tangents.
//This is because the triangle has been mirrored when going from tangent space to object space.
//reverse tangents if necessary
Vector3 tangentCross = tangent.CrossProduct(binormal);
if (tangentCross.DotProduct(normal) < 0.0f)
{
tangent = -tangent;
binormal = -binormal;
}
return(tangent);
}
